Hetero-double-helix formation by an ethynylhelicene oligomer possessing perfluorooctyl side chains

Monomeric to pentameric (P)-ethynylhelicene oligomers possessing perfluorooctyl side chains were synthesized. The circular dichroism (CD) and vapor pressure osomometry (VPO) studies indicated the formation of a helix-dimer for the (P)-pentamer, for example, in trifluoromethylbenzene at 5 degrees C at concentrations above 2 x 10(-6) M. Compared with a (P)-pentamer possessing decyloxycarbonyl side chains, the perfluorooctyl (P)-pentamer exhibited lower solubilities in organic solvents, formed a thermodynamically more stable helix-dimer, and exhibited a mirror image CD spectrum. The perfluorooctyl (P)-pentamer formed a hetero-helix dimer with a decyloxycarbonyl (M)-pentamer but not with a (P)-pentamer. It indicated higher stability of the hetero-helix dimer over the homo-helix dimers.     

Detection limit in the (pX,X) technique—A novel method for trace element analysis

The (pX, X) technique is a very reliable tool for trace element analysis when large amounts of a neighboring element are present. This paper describes the experimentally determined detection limits of some available sources of GaAs, Ge and Zr, to evaluate the utility of this technique. The theoretical detection limits calculated with a computer program are also described.     

Recent advances in reactions between arynes and organosulfur compounds

The recent progress made on transformations involving the reactions between aryne intermediates and organosulfur compounds has been reviewed. A wide variety of aromatic organosulfurs are now synthesizable by generating arynes in the presence of organosulfur compounds. Organosulfurs have distinctive reactivities with arynes, which depend on the sulfur atom’s valence state, that is, S(II), S(IV), and S(VI), as well as the presence or absence of other intra- or intermolecular reactive moieties. These novel transformations have enabled the diversity-oriented synthesis of unique aromatic organosulfurs that were once difficult to prepare by the conventional methods, paving the way for the development of molecules that are beneficial across numerous disciplines, including pharmaceutical science and materials science.     

Total synthesis of tylonolide,an aglycone of tylosin

The total synthesis of tyionolide, a 16-membered-ring aglycone of a macrolide antibiotic, tyiosin, has been accomplished by coupling two segments of C1-C10 and C11-C17 portions, which are stereospecifically derived from D-glucose.     

1,3-Addition of silyl enol ethers to nitrones catalyzed by mesoporous aluminosilicate

Mesoporous aluminosilicate (Al-MCM-41) was found to be an effective and reusable catalyst for 1,3-addition of silyl enol ethers to nitrones. The reaction proceeded under mild reaction conditions to afford the corresponding β-(siloxyamino)ketones in high yields. Furthermore, a unique chemoselectivity of a nitrone over an aldehyde and an acetal, which are more reactive toward silyl enol ether in the presence of Al-MCM-41 than a nitrone, was observed.     

Highly polarized very cold neutrons through a permanent magnet quadrupole

We obtained highly polarized very cold neutrons through a quadrupole magnet with a large aperture. When neutrons go through a quadrupole magnet, parallel-spin neutrons are attracted to the magnet axis and anti-parallel-spin neutrons are repelled off the axis. Therefore, the neutrons through a sufficiently long quadrupole magnet have completely parallel-spin. At the downstream of the quadrupole magnet, we placed another quadrupole magnet to divide neutrons into two regions depending on their spin directions. We obtained the neutron polarization from the integrated count of the two regions and found it was 99.88±0.09 (stat.)±0.05 (syst.)%.     

Controlled self-assembly of multiple diastereomeric macrocyclic boronic esters composed of two chiral units

Controlled construction of four out of five diastereomers of macrocyclic boronic ester was achieved in high yield by utilizing the self-assembly of two chiral components with the proper choice of reaction conditions. Three diastereomers could be constructed as enantiopure forms by properly changing the chirality combination between the two building blocks. Furthermore, the methodology could be applicable to the three-component self-assembly of enantiopure macrocyclic boronic esters having two different diboronic acid moieties.     

Photodegradation of environmental mutagens by visible irradiation in the presence of xanthene dyes as photosensitizers

The photodegradation of environmental mutagens, such as 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeAαC), and 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ), was investigated by visible irradiation in the presence of xanthene dyes as photosensitizers. Although the environmental mutagens themselves were very stable during visible irradiation under the conditions in this study, they were effectively photodegraded in the presence of the xanthene dyes (erythrosine, rose bengal, and phloxine). Moreover, photodegradation of the mutagens was further enhanced for xanthene dyes loaded onto a water-soluble diethylaminoethyl (DEAE)-dextran anion-exchanger via ionic interactions (xanthene-dyeDEX). Photodegradation was inhibited by O2 removal from the reaction solution. In ESR spin-trapping experiments using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a trapping reagent, signals characteristic of DMPO-?OH (hydroxyl radical) were observed in the presence of xanthene-dyeDEX. These results suggest that reactive oxygen species derived from O2, such as singlet molecular oxygen (?1O2) and/or ?OH, were active participants in photodegradation of the mutagens in the presence of xanthene dyes or xanthene-dyeDEX.     

Effective dispersion of fullerene with methacrylate copolymer in organic solvent and poly(methyl methacrylate)

Dispersion of fullerene, C₆₀, by addition of polymethacrylate dispersant in methyl methacrylate (MMA) and incorporation of C₆₀ into poly(methyl methacrylate) (PMMA) were investigated. Copolymers synthesized by radical copolymerization of MMA and 2-naphthyl methacrylate (NMA), poly(MMA-co-NMA), effectively dispersed C₆₀ in MMA to form clusters of 20?nm. In these cases, addition of minimal 110 naphthyl groups per unit C₆₀ molecule afforded to give clusters with minimum of 20?nm sizes. Furthermore, block copolymers, poly(MMA-b-NMA) with MMA/NMA mole ratio from 12:1 to 20:1, also efficiently dispersed C₆₀ to give formation of clusters of 20?nm size by addition of minimal 40 naphthyl groups per unit C₆₀ molecule, which was corresponding to approximate nine layers of naphthyl group in block copolymer adsorbed on the surface of the cluster. Hybrid films of C₆₀/PMMA, prepared by casting of C₆₀-dispersed solution containing PMMA, exhibited absorbance at 400?nm linearly increased with C₆₀ content.